Google send you a .acsm file, which Adobe Digital Editions trades for the .epub
you actually purchased, after doing the DRM thing. In my case, the DRM step
didn’t work, no matter which way I did it. I got a refund. It’d be one thing
if I got a locked up .epub, I could just
remove the DRM,
but this file is useless.

And since I’m a nice guy, I emailed Stross and told him that I’m going to
either download an ebook copy illegally, or just purchase the book used when the
price drops.